1. Field of the Invention
This invention relates to lock assemblies of the type having a housing with a key-operated plug that is rotatable within the housing about an axis to effect movement of a latch element and, more particularly, to a lock assembly wherein the key plug can be removed to facilitate interchange of key plugs and/or repair of a key plug.
2. Background Art
It is well known to construct lock assemblies that are actuated through a key operated plug. The plug is rotatable guidingly within a housing to effect movement of a latch element. This type of actuating mechanism is used on conventional door knobs, latches, and deadbolts. It is also used on paddle latches on closures for motor homes and tool boxes. A similar actuating mechanism is also used on furniture locking systems.
Typically, the plug has a plurality of wafers that are movable transversely to the plug axis between extended and retracted positions by insertion of a key into an axial keyway in the plug. In an extended position, the wafers project into undercut guide slots in the housing in which the plug is journalled for rotation. With the wafers extended, the plug is fixed against rotation relative to the housing. By extending a key into the keyway through the plug, the wafers can be retracted to allow rotation of the plug mound the plug axis to effect movement of a latch element operatively connected to the key plug.
One desirable feature of this type of lock assembly is the ability to remove and replace the key plug. This allows the lock assembly to be "re-keyed" in the event that the system security has been compromised. This also permits universal construction for the housing and selective "keying alike" or diverse keying as may be the desire of the end user.
It is a goal of designers of lock assemblies with removable key plugs to provide a structure that has high integrity, i.e. is highly secure, yet one which can be manufactured efficiently and at an affordable price.
Examples of known lock assemblies with removable key plugs are disclosed in each of the following patents - U.S. Pat. No. 1,922,889, to Falk; U.S. Pat. No. 3,260,080, to Wellekens; U.S. Pat. No. 3,863,476, to Patriquin; U.S. Pat. No. 4,398,405, to Patriquin; U.S. Pat. No. 4,404,825, to Dixon et al; and U.S. Pat. No. 5,235,832, to Lux et al.
One desirable feature in Falk is that the plug part 11 can be pre-assembled to the outer housing. The plug pall 11 remains at all times operatively associated with the housing 10. If it is desired to change the keying for the system, only the plug part 12 need be removed from the housing 10 and separated from the part 11. This reduces the cost and complexity of the replaced part and does not require re-setting or adjustment of the plug part 11 once the plug part 12 is moved.
Falk maintains the plug part 12 operatively on the housing 10 through a radially projecting disk/wafer 28 which moves into a radial groove 31 in the housing. Formation of the internal groove 3 1 adds considerably to the expense and complication of manufacture of the housing 10.
A further problem with some prior an locks, using a wafer and guide slot combination to prevent axial withdrawal of the associated plug, is that this type of system can be relatively easily "picked". Unauthorized entry may be accomplished by prying the locking wafer to a retracted position, as with a sharp instrument, such as a paper clip, or the like. Once the locking wafer is retracted, the key plug can be withdrawn axially from the housing to gain unauthorized access through the previously locked closure/drawer.
While the above type of system may facilitate interchange of key plugs, such systems may at the same time facilitate a security breach.